JPS5462670A - Starting device for discharge lamp - Google Patents

Abstract

PURPOSE:To stabilize the actuation of a discharge lamp regradless of the fluctuation of the supply voltage by connecting a trigger element in parallel to a capacitor to be provided to a gate circuit of a thyristor in an actuating pulse generating circuit. CONSTITUTION:During a positive half cycle of an a.c. voltage applied to a lamp 20, a thyristor T20 is triggered through a resistor R21, a diode D22 and a capacitor C22. A capacitor C21 is discharged through the thyristor T20, the power supply E20 and the primary coil of a stabilizer B20, whereby a high voltage pulse is induced across the stabilizer B20 to light the lamp L20. During a negative half cycle, the capacitor C21 is charged through a diode D21 with the polarity shown in the diagram. During the next positive half cycle, the thyristor T20 is triggered again. The resulting pulse legs the cycle of the a.c. voltage by some degree due to some residual electric charge in the capacitor C22. This process is repeated until the voltage developed across the capacitor C22 reaches the breakover voltage of a two- terminal-thyristor S20. Then the capacitor C22 is discharged and the same process is repeated again.